" Click the menu button  and select Settings.
   In the General panel, scroll down to the Tabs section.
   Make sure the box next to Enable Container Tabs is checked. "

I am attempting to configure the "Simple Tab Groups" extension (having failed to get any help working with the more complicated Sideberry). Following instructions in firefox's "How to use Containers" article: viz: Enable Firefox containers " Click the menu button and select Settings. In the General panel, scroll down to the Tabs section. Make sure the box next to Enable Container Tabs is checked. " The "enable Container Tabs" is at the end of the list and is paler type with the box appearing checked; clicking it does not change it. Does that mean it is already self-enabled so that I cannot click it ? This might seem a stupid question but, I am only trying to follow directions! (Now you see why, without directions, I couldn't set up Sideberry. GitHub people wouldn't even answer my questions. I'm not a coder. Thanks